Well Incipio must have read my "complaint" here on the forum because I just received an email saying that the cover shipped
And I just got out of the chat with them (an awesome feature BTW) and they told me that the nylon cover weights 5 ounces (~140g) and the synthetic leather version only weights more 0.something (they weren't specific how much above 5 onces the cover was) but it's still a few ounces lighter than the Kindle itself.